THE CENTRAL TEGMENTAL BUNDLE AN ANATOMICAL AND EXPERIMENTAL STUDY IN THE MONKFAY JOSE BEBIN‘ Laboratory of Comparative Neurology, Department of Anatomy, University of Michigan, Ann Arbor THREE FIGURES INTRODUCTION In the brainstem of higher mammals there exists a very con- spicuous and important tract linking the diensephalon to the inferior olivary nucleus. This system, that reaches its highest development in primates and man, was described for the first time by von Bechterew (1885) who called it “centrale Hauben- bahn” indicating its origin and termination. It is a fact, however, that nowadays the origin of this system is the object of discussion and controversy among anatomists. This is the reason we prefer to use the name “central tegmental bundle” because the name does not imply any specific origin or termination and yet, nevertheless, emphasizes a most important relation of the tract, that is, that it courses through the central portion of the tegmentum of the brainstem. For many years, only its anatomical structure and relations attracted the attention of investigators, but its functional ac- tivity and its clinical signifkance met with little interest. Foix et al. (’26) established a direct relationship between a lesion of this system at pons levels (with the consequent degeneration of the inferior olive) and a curious syndrome called palatal nystagmus or palatal myoclonus. The work of Foix et al. inaugurated a fruitful period of clinico-anatom- * Present address: Henry Ford Hospital, Detroit, Mich. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the University of Michigan. 1953. 287 288 JOSE BEBIN ical studies upon the central tegmental bundle and the syn- drome of palatal nystagmus. As a result of their work very interesting and ingenious physiopathological theories have been proposed. The advance in the clinico-anatomical field brought new questions to mind that neither the clinical nor the anatomical investigations were able to solve satisfactorily. The discovery and application of stereotaxic instruments to the study of the physiological activity of the central nervous system opened new horizons along the lines of neurophysiological research. The neurophysiological methods have been applied to the study of the central tegmental bundle. The works of Ranson et al. ('42), and many others, demonstrated that the teg- mental gray of the brainstem and the tracts which course through it seem to constitute coordinating centers for the activity of the facial, glossal, palatal and laryngeal muscula- ture. Either destruction or stimulation of the central teg- mental bundle resulted in the production of abnormal rhyth- mic movements similar to those seen in patients with a lesion of the central tegmental bundle or inferior olive, offering a very important contribution to the understanding of this curious syndrome. In spite of the all important advances in the anatomical, physiological and clinical aspects of the central tegmental bundle and the palatal nystagmus syndrome, multiple other questions remain unanswered. What are the anatomical rela- tions between the central tegmental bundle, the cranial nuclei and the reticular gray9 What is the physiological significance of the central tegmental bundle? What is its role in the so-called palatal nystagmus? These problems have been the source of our curiosity and interest in making this experi- mental and anatomical study of the central tegmental bundle in an attempt to understand the complex functions of this system. ACKNOWLEDGMENTS The author wishes to express his sincere gratitude and appreciation to Professor Elizabeth C. Crosby with whose en- THE CENTRAL TEGMENTAL BUNDLE 289 couragmnent and unending assi,stance this study was planned and executed, to Dr. R. Yoss for his help during the surgical procedures, and to Mr. George Smith for his technical as- sistance in the preparations of the microscopical material. MATERIALS AND METHODS The animals used in this study were Macaca mulatta and Macacus cynomolgus. The normal anatomy of the brain of Macaca mulatta was studied in preparations from the Huber Comparative Neurological Collection stained by the Weil technique. The experimental material was prepared by the Marchi method using the Swank and Davenport ('35) modi- fication. This technique reveals only degenerating myelinated fibers. The technical difficulties and apparent optimal stain- ing times for various fiber systems, of necessity, limits the conclusions which can be drawn from a study of this nature. Ten lesions were placed, 4 animals being used for the experi- ments. The McCulloch stereotaxic instrument was employed for making the lesions under ether anesthesia. The stimulation of the central tegmental bundle was carried out under variable depths of ether anesthesia using a minimal faradic current from the Grass stimulator. The results of electrical stimulation are modified by many factors such as temperature, blood supply, shock, flow of cerebrospinal fluid, type and depth of anesthesia and type and intensity of stimulating current (see also Hines, '44). The lesions of the central tegmental bundle in the tegmentum of the brainstem were produced by an insulated needle through which a mild cauterizing electric current was passed. In all instances, preoperative and postoperative testing of the animals was carried out and included examination of reflexes, muscle tone, cranial nerves and careful inspection of the mouth and palate. All the monkeys studied were sacrificed between the 14th and 20th postoperative days. After inducing surgical anesthesia with ether or sodium pentothal, the thoracic cavities were rapidly opened bilaterally and the arterial systems perfused with 500 to 1000cm3 of 290 JOSE BEBIN 10% formalin. The brains with attached cervical cords were removed carefully; in all instances the fixation was excellent. SURVEY OF LITERATURE In 1885 von Bechterew, working at Flechsig’s Laboratory, described a system of fibers connecting the cerebrum to the inferior olive which he called the ‘‘ centrale Haubenbahn. ’ ’ This is a system of fibers the course of which can be followed longitudinally through the brainstem from the caudal part of the diencephalon to the inferior olivary nucleus. This system had been previously mentioned by others, such as Stilling (1846) Schroeder van der Kolk (1859) but without giving a precise description. According to von Bechterew, this bundle begins in the caudal end of the diencephalon, around the gray substance of the third ventricle; from this point it follows a descending course through the central por- tion of the tegmentum of the brainstem. It is situated, first, ventromedial to the medial longitudinal fasciculus, then, at pontine levels, dorsal to the medial lemniscus and superior olivary nucleus, and finally, at the medulla levels, in the olivary capsule and hilus of the inferior olivary nucleus. Some of the fibers probably continue caudally in the olivo-spinal system. Since the description by von Bechterew, we find numerous anatomical studies in the medical literature which add very little to clarify our understanding of this bundle. Its existence is generally accepted, but the number of fibers included in it by the different writers varies from the components given in the original description, and the name has changed from writer to writer. ‘ ‘Fasciculus thalamo-olivaris ” was the name used by Edinger ( ’11), Beccari ( ’43), Rasmussen ( ’45) ; ‘‘fas~i~ulusthalamo-bulbaris ” was Castaldi’s ( ’23) term ; and “fasciculus anulo-olivaris” was Mettler’s ( ’44)name for it; Woodburne, Crosby and McCotter (’46) called it the “pallido-incerto-olivary system. ” These different termin- ologies indicate the disagreement among writers as to the exact place of origin of this system. This disagreement is TEE CENTRAL TEGMENTAL BUNDLE 291 easily understood, since human cases of the degeneration of this complete system have not been observed, and the histo- logical methods have not been successful in clarifying its origin in normal human material. Several hypotheses dispute the origin of the system but they fall into 4 fundamental groups. The first hypothesis places the origin in the corpus striatum, the second in the thalamus, the third in the tegmentum of the midbrain, and the fourth in the red nucleus of the midbrain. Regarding the first hypothesis, Flechsig ('20) was one of the early workers to offer the opinion that the central teg- mental bundle derived most of its fibers from ansa lenticularis. Probst ( '03) advanced the idea that some of the fibers of this bundle emanated from the diencephalon and continued to the inferior olive. Winkler ('33) considered this system as a strio-olivary pathway but thought, in disagreement with Wallenberg ('22)' that its fibers arose in the pallidum and not in the neostriatum. Winkler also believed that a consider- able component of fibers of pallido-rubral origin coursed downward through the tegmentum of the midbrain with this system but did not end in the inferior olivary nucleus but in the reticular substance of the rhombencephalic tegmentum. This point of view was accepted by Weisschedel ('37), who based his conclusions upon an investigation of human material from subjects whose ages ranged from 19 to 40 years. He held that the central tegmental bundle is made up of several components: a main bulk of rubro-olivary, and other ac- cessory pallido-olivary fibers, pallido-rubro-reticular fibers and reticulo-reticular fibers. Many writers deny